_{Alternating Current,(AC) is a current that changes direction cyclically, passing first in one direction, then in the other through a circuit. Such alternating currents are produced by generators and other such voltage sources whose polarities alternate between a positive direction and a negative direction rather than being fixed in a constant direction as with DC sources. Alternating currents, by convention, are called AC currents and alternating voltages are called AC voltages.}

_{The variation of an AC voltage or an AC current over time is called a waveform. Since these waveforms vary with time, AC supplies are designated by v(t) for voltage, and i(t) for current. Here, t represents time.} _{There are many different types and shapes of waveform but the most fundamental is the sine wave (also called sinusoid). The sine wave or sinusoidal AC waveform is the voltage and current waveform shape of the AC power source that supplies energy to our home.}

_{The sine waveform starts at zero, increases to a positive maximum (peak), and then decreases to zero, changes polarity, increases to a negative maximum, and then returns back to zero. One complete variation between the same points on the waveform is referred to as a cycle. Since the waveform repeats itself at regular intervals over time, it is called a periodic waveform.}

_{The calculation of average, R.M.S., form factor, and crest factor can be used with any type of periodic waveform including Triangular, Square, Sawtoothed, or any other irregular or complex voltage or current waveform shape.}

## Waveforms if different types (with wave diagram)

In the following sections, 6 types of AC waveforms are shown using wave diagrams.